MYSQL DATE function runs insanely slower in LEFT JOIN

Question

When adding a line:

LEFT JOIN core_records_sales as sales ON DATE(appointments.date) = DATE(sales.date_sold)

At my request, this speeds up the time for the script to run from 8 seconds to 2-3 minutes.

Will there be any data causing this problem, or am I implementing this function incorrectly?

I need to use DATE () because I need them to be on the same day, but the date fields are DATETIME

Answer 1

This is almost certainly a problem with the assignments.date field index. Adding the use of the DATE () function ensures that the index cannot be used, forcing a table scan.

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Answer 2

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Answer 3

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